Sound recording apparatus and arrangement for use therewith



Jan. 12, 1932. 1 ROUND 1,840,795

SOUND RECORDING APPARATUS AND ARRANGEMENT FOR USE THEREWITH' Filed Jan. 28, 1931 Patented Jan. 12, 1932 vmrsn sTA'rESjPAT HENRY JOSEPH ROUND, or LONDO ENGLAND, AssreNoa T MARGONIS wrnnnsss TELEGRAPH COMPANY LIMITED, or "LONDON, rNaLe n.

SOUND RECORDING APPARATUS AND ARRANGEMENT roausn Tee-s men Application filed January 28, 1931, Serial No. 511,906, and in'Grea't Britain January 23, 1930.

This invention relates to sound recording recording sound on films.

* and Figs. and Gshowcircuit diagrams for the oscillograph of my invention. I Referring to theaceompany drawings, and

The invention has for its principal object r to provide a recording oscillograph or the like which cannot easily be over-loaded andwhich is especially' adapted for producing upon a film an accurate sound record, and which shall be sensitive but not easily overin loaded and capable of dealing satisfactorily with widely varying amplitudes; According to' this invention, a moving iron oscillograph for use in sound recording'comprises a moving member consisting of "a small steel or similar spring reedrigidly carried at or near one end by acomparatively large block of metal and carrying a relatively stilt block of magnetic material upon which is. mounted a mirror, the free spring 'l'engthumeters; free spring length where bending takes place being small (of takes placeabout mm.; block 8 of'magthe order of about mm. to about 1 mm.) so netic material mm. thick, 2 mm. wide and that in use the movement of the 'mirroris l f ymmpwith spike extension as illustrated, largely rotary and said armature being the' spike being about 2mm. long, damped to prevent excessive amplitude at .1 :A'rubber damping block 3 is firmly stuck resonance by means of small rubber or like on to the spike i. Saidblock may beabout block carried at or near the free end thereof. ,5 mm; to 1. min; cube, the dimensions being Preferably meansare providedfor adjust- 7 not very important over a wide range of size. =The7reedsystem (IDCIUSIVG of the mirror) ing the polarizating magnetization of the may, 1n most cases, be so made asto have oscillograph so that the response of the arma- 1 ture for amplitudes exceeding the minimum aperiod at about 6,500 cycles per second, but 80 amplitude shall be as'linear as'possible. .-i in certain cases, where sensitiveness is of great importance, thevalue may vbe reduced My invention will be more clearly underas low'as-4,500' cycles. 1. I

The mirror is attached to 'a non-bending stood from the following specification by reference to the accompanying drawings j which illustrateone form of oscillograph acp f imovlng'membel the block cording to my'invention and h r in; 8) and-this prevents distortion of the reflect I Fig. l-is'a characteristic curve explanatory ed A I I Y of the principle of operation of the oscillo 'rlhe K L F- J d t graph of invention, Fig. 2 shows the q d. h Smgle Q 7 block, reed mirror and damping arrange-1 f tmcbsublected permanent or ments for the oscillograph; Fig 3 showsin f i ifi fi g i fi a? schematic form the general arrangements of j 21 553 3; 2x5? 5 the magnetic circuit of the oscillograph; Fig.1 ghich is in i d a olariz i l lg poll 6 and ments in association with the magnetic s ewz gitggiii i ii g. gf gifgfl 13: 355,-,

h of t oscillograph; Fig?- PP I Xi- :po1e 8., On thepole pieces 7+7 are mounted 'mately only half of the magnetic system is operating coils 9 -9 towhieh thecurrents or so shown for the sake of clarity in thefigure) voltages intended to be recorded are fed; The W l more particularly to Figs. 2, 3 and 4c thereof, the oscillograph comprises a mainmoving .1 member consisting of an armature or reed 1 of steel or other resilient material, to which is fixed a block 8 ofmagnetic material which should be sufficiently thick to resist bending, and on this block is arranged a mirror- 10 and.- a .spikez,thevlatter being made in the case shown asan extension ofthe blmk 8 and in one piece therewith the reed l is rigidly attached at or near "one end .to a comparatively large block 2 of metal. v r .1 V The following are. dimensions which have been successfully employed in practice Width of spring armature 1 about 2 milliwhere bending 7 magnetic system including the pole pieces may be made of a high permeability iron such as that known under the registered trade mark Numetal or one of the recently discovered nickel-iron high permeability metals and gaps of non-magnetic material may be inserted between the pole pieces 7-7 and the remainder of the magnetizing circuit, the poles themselves being kept to as small a length as possible.

An instrument as above described will have a characteristic which consists of a line which is approximately strai ht for the middle portion of its length and curved at the two ends, the two curved ends corresponding to the conditions of low magnetization and approximate saturation. Such a characteristic curve is shown in Fig. 1 oi the accompanying draw ings, in which curve the ordinates are units of deflection (D) and the abscissa units of polarization magnetization (PC). The instrument should be operated over the middle or approximately straight portion of the characteristic with amplitudes which are not sufliciently large to swing into the curved portions; i. e. referring to Fig. 1, the central operating point should be point P on the curve and the operating amplitudes should lie roughly betwen the parallel broken lines The gaps of non-magnetic material are shown at 1111 and may conveniently consist of interposed brass pieces. This arrangement minimizes the efiect known as zero wandering i. e. the tendency for the moving member not always to return exactly to the same zero position upon the cessation of current through the operating coils. The small mirror 10 may be utilized in any well known to change one mirror for another in a device as above described does not result in any v serious alteration of the natural period providing the mirrors interchanged are of ap-, proximately the same size.

An oscillograph as above described gives a very uniform amplitude response plotted against operating current over the frequency 7 range up to the resonant point.

Electric currents corresponding to sound .and obtained from an amplifier associated with a microphone are fed to the operating coils so as to induce corresponding vibrations in the moving member. A slot of intense light obtained in any convenient manner is projected on the mirror carried by the moving member and reflected therefrom to fall upon a moving photographic film surface.

The current fed through the energizing coils is first passed through an electrical network so that the amplitude of the vibrations of the armature will be approximately the same for a given microphone output at any frequency within the audible frequency range. This requirement is approximately obtained when the current through the coil of the network is approximately proportional to the grid potential applied to the last valves (i. e. the power valves) of the thermionic amplifier which is controlled from the microphone and whose output is fed to the coil and network. A preferred method of obtaining this required constancy oi current consists in constituting the network by a series resist ance shunted by a condenser so as effectively to balance out the self-inductance of the coil. Circuit arrangements suitable for accomplishing this desired result are shown in Figures 5 and 6. In these figures C represents capacity, L inductance and E- resistance while the operating coils of the oscillograph are diagrammatically represented at QC. Alternatively the operating coils may be made part of a low pass filter circuit adapted to give constant current.

It is of importance to be able to set the polarizing magnetism exactly, in oscillographs of the kind in question and where electro-magnetic polarization is employed this may be effected by adjusting the current in the polarizing windings. here permanent magnets are employed it is useful to provide a magnetic shunt arrangement and/or an air gap adjustment between the poles and the magnet for the purpose of obtaining correct magnetic setting.

Wheat 1 claim is zr 1. A moving iron instrument for use in sound recording and including a moving niember consisting of a small spring reed rigidly carried adjacent one end by a relatively large block of metal, a relatively still block of magnetic material carried on said spring reed, a mirror surface upon said last mentioned block for reflecting light rays and a small block of resilient material mounted upon said spring reed adjacent the free end thereof "for damping excessive amplitude at resonance the free spring length of said spring reed where bending takes place being relatively small and of the order of mm. to about 1 mm. and means for magnetically controlling the movement of said moving member in accordance with sound vibrations. j

2. A moving iron instrument for use in sound recording and including a moving "member consisting of a small steel spring reed rigidly carried adjacent one end by a relatively large block of metal, a relatively stifi block of: magnetic material carried on -se said springreed, a mirror surface upon said I last mentioned block for'refiecting light rays and a small block 'of rubber mounted upon said spring reed adjacent the: free end thereof to damp excessive amplitude at resonance,

- the free spring length of said spring reed 1 Where bending takes place being of the order rigidly of mm. to about 1 mm. and means for magnetically controlling the movement of said moving member in accordance W1th sound vibrations.

3. A moving iron instrument for use in sound recording and including a moving member consisting of a small spring reed carried adjacent one endrby a relaof metal, a relatively stiff tively large block carried on said block of magnetic material spring reed, a mirror surface upon said last mentioned block for reflecting light rays, a small block of resilient material 'mounted upon said spring reed adjacent the free-end thereof to damp excessive amplitude at resonance, the free spring length of said spring reed Where bending takes i place being of the order of mm. to about 1 mm., a magnetic polarization system means for adjusting the polarizing magnetism thereof and me ans for magnetically controlling the movement of said movingmember in accordance With sound vibrations V i. A moving iron instrument for use in sound recording and including a moving member consisting ,ofia small steel spring reed rigidly carried adjacent one end by a relatively large block of metal, a relatively stifi' block of magnetic'material carried on said spring reed, a-mirror surface upon said last mentioned block for reflecting light rays,

a small block of rubber mounted upon said spring reed ad acent the free end thereof to damp excessive amplitude at resonance, the "free spring length of said spring reed Where bending takes place being of the order of mm. to about 1 mm., a magnetic polarization mentioned block for reflecting light rays and a small block of resilient material mounted upon said spring reed adjacent the free end thereof to damp excessive amplitude atresonance, the free spring length of said spring reed Where bending takes place being of the order of mm. to about 1 mm. and means for magnetically controlling the movement of said moving member in accordance Witl sound vibrations.

- 6. A moving iron instrument for use in sound recording and including a moving member dimensioned and adjusted to have its natural period above 4500 cycles per second and consisting of a small steel'spring reed rigidly carried adjacent one end by a relatively large block of metal, a relatively stiff block of magnetic material carried on said spring reed, a mirror surface upon said last mentioned block for reflecting light rays, a small block of rubber mounted upon said spring reed adj acent'the freeend thereof to damp excessive amplitude at resonance, the freespring length of said spring reed Where bendin takes places being of the order of mm. to about 1 mm, a magnetic polarization system means for adjusting the polarizing magnetism thereof and means for magnetically controlling the movement of said 'moving member in accordance with sound vibrations.

7; A moving iron instrument for use in sound recording and including a moving member consistin of a small steel SOI1I10 b J. t:

reed rigidly carried adjacent one end by a relatively large block of metal, a relatively stiff block of magnet1c material carried on said spring reed, a mirror surface upon said last mentioned block for reflectlng light rays,

a spike carried by said reed and. a small block of rubber fixed upon saidspring reed adja cent the free end thereof to damp excessive amplitude at reasonance, the free spring length of said spring reed Where bending takes place being of the order of mm. to about 1 mm. and means for magnetically controlling the movement of said moving mem-' her in accordance With sound viorations.

8. A moving ironinstrument for use insound recording and including a moving member dimensioned and adjusted to have its natural period above 4500 cycles per sec-o 0nd and consisting of a small steel spring reed rigidly carried adjacent one end by a relatively large block of metal, a relatively stiff block of magnetic material carried on saidspring reed, a mirror surface upon said last mentioned block for reflecting light rays,

a spike carried by said reed, a small block V of rubber mounted upon said spike for damping excessive amplitude of said block of magnetic material at resonance, the free spring length of said spring reed WherebencL ing takes place being of the order of mm. to about 1 mm., a magnetic polarization system means for adjusting the polarizing magnetism thereof and means for magnetically controlling the movement of said moving-V member in accordancewith sound vibrations.

" 9. A moving iron instrument for use in sound recordmgand lncludlng a moving member consisting of a small spring reed rigidly carried adjacent one end by a relatively large block of metal, a relatively stiff block of magnetic material carried on said spring reed, a mirror surface upon said last mentioned block for reflecting light rays, a small block of resilient material mounted upon said spring reed adjacent the free end thereof to damp excessive amplitude at resonance, the free spring length of said spring reed where bending takes place being of the order of mm. to about 1 mm., a magnetic system including gaps or spacing in the magnetic pa h thereof and m ans connected with said magnetic systen'i for controlling the effect thereof upon s moving member.

10. A moving iron instrument for use in sound recording and including a moving member consisting of a small spring reed rigidly carried adjacent one end by a relatively large block of metal, a relatively still block of magnetic material carried on said spring reed, a mirror surface upon said last men ioned block for reflecting light rays, 21 small block of resilient material mounted upon said spring reed acent the free end thereof to damp excessive amplitude at resonance, th free L ng length of said spring reed where bending takes place being of the order of 1 mm. to about i inn, a magnetic system including magnetic shunt means across the magnetic path thereof and means connector with said magnetic system for controlling the eflect thereof upon said moving member.

11. A moving iron instrument for use in sound recording and including a moving member consisting of a small spring reed rigidly carried adjacent one end by a relatively block of metal, a relatively stiff block of magnetic material carried on said spring reed, a mirror surface upon said last mentioned block for reflecting light rays, a small block of resilient material mounted upon said spring reed adjacent the free end thereof to damp excessive amplitude at resonance, the free spring length of said spring reed where bending takes place being of the order of mm. to about 1 mm., a magnetic system including polar members of high permeability material and means connected with said magnetic system for controlling the effect thereof upon said moving member.

12. In combination, a moving iron instrument for use in sound recording and including an operating coil, a moving member consisting of a small spring reed rigidly carried adjacent one end by a relatively large block of metal, a relatively still block of magnetic material carried on said spring reed, a mirror surface upon said last mentioned block for reflecting light rays, :1 small block of resilient material mounted upon said spring reed adjacent the free end thereof to damp excessive amplitude at resonance, the free spring length of said spring reed where bending takes place being of the order of X mm. to about 1 mm, an electrical network arranged to balance out the self inductance of said coil and a sound control circuit connected with said network.

18. In combination, a moving iron instrument for use in sound recording and including operating coils, a moving member consisting of a small spring reed rigidly carried adjacent one end by a relatively large block of metal, a relatively stiff block of magnetic material carried on said spring reed, a mirror siuface upon said last mentioned block for reflecting light rays, a small block of resilient material mounted upon said spring reed adjacent the free end thereof to damp excessive amplitude at resonance, the free spring length of said spring reed where bending takes place being of the order of mm. to about 1mm., and an electrical network consisting of resistance shunted by capacity in series with the operating coils of said instrument and a sound control circuit connected with said network.

14. In combination, a moving iron instrument for use in sound recording and including an operating coil, a moving member consisting of a small spring reed rigidly carried adjacent one end by a relatively large block of metal, a relatively stiff block of magnetic material carried on said spring reed, a mirror surface upon said last mentioned block for reflecting light rays and a small block of resilient material mounted upon said spring reed adjacent the free end thereof to damp excessive amplitude at resonance, the free spring length of said spring reed where bending takes place being of the order of mm. to about 1 mm., an electrical network connected with said operating coil and a sound control circuit connected with said network, said electrical network being proportioned for balancing out the self inductance of said operating coil.

In testimony that I claim the foregoing as my invention I have signed my name this 16th day of January, 1931.

HENRY JOSEPH ROUND. 

